The present invention relates to a fractional horsepower electric motor assembly, and more specifically to a motor housing that includes a gasket integrally attached to the motor brush holder and motor housing assembly.
Fractional horsepower electric motors are used in numerous automotive applications. For example, electric motors are used in automotive seat adjustment mechanisms, side-view mirror adjustment assemblies, and windshield wiper control mechanisms.
In the last several years, significant engineering effort has been expended on reducing the cost, and increasing the reliability of fractional horsepower electric motors used in automotive applications. One way to reduce the cost is to eliminate as many separate components as possible. Further, one way to increase motor reliability is to reduce or eliminate the potential for moisture to enter the motor assembly.
As noted above, consistent, reliable motor performance requires that the motor assembly be isolated within a watertight housing. In a standard motor assembly, a motor, including electrical brushes, a commutator, and magnets, is located in a motor housing. In particular, electrical brushes are mounted in a brush holder assembly that is inserted around the commutator. The commutator and brush holder are then inserted within the motor housing prior to the motor housing being attached to a gear housing that contains at least one gear driven by the motor. The interface between the motor housing and the gearbox housing is a primary entry pathway for moisture.
The junction between the motor housing and the gearbox housing is conventionally leakproofed by compressing a flat gasket or an o-ring between the two housings when they are joined together. Specifically, before attaching the motor housing to the gear housing, a separate gasket or o-ring is placed on a mating surface of, for example, the motor housing. A corresponding opposed mating surface of the gearbox housing is then placed in facing relationship to the motor housing mating surface, thereby compression the gasket or o-ring between the mating surfaces. It is difficult to properly locate the gasket or o-ring so that it provides an optimal seal. Moreover, gaskets have a tendency not to lay flat, but rather to curl, and o-rings tend to twist and/or roll up, resulting in imperfect leakproofing of the junction between the housings.
Moreover, separate gaskets or o-rings impair the production of motor assemblies because they are often attached to the housings by hand. The alignment of a flat gasket around the outer circumference of the housing can be a rate limiting step in an assembly line operation. This is even more true of an o-ring which typically must be aligned within a circumferential groove preformed in one of the mating surfaces.
Consistent, reliable motor performance is further dependent upon proper alignment between the brushes, the commutator, and the magnets in the motor. Conventionally, this is accomplished by locating and fixing the brush holder within the motor housing with fasteners, usually with screws. Attaching the brush holder assembly within the motor housing in this fashion requires additional machining and more precise tolerances to ensure the consistent and accurate positioning and alignment between the brushes, the commutator, and the magnets. Additionally, depending on their positioning, the fasteners may introduce additional moisture-entry pathways into the motor assembly.
Thus, a mechanism is desired that provides proper alignment of all component parts of the motor without the use of separate fasteners, and without adversely impacting the watertight integrity of the motor assembly.
Accordingly, the present invention provides a motor housing assembly that includes a motor housing, a brush holder assembly, a gasket, and a gearbox, such that the brush holder assembly may be fixed in position at a junction between the motor housing and the gearbox. In one preferred embodiment, a gasket is mechanically attached to the brush holder assembly via detents, and is compressed between the motor housing and gearbox when the two are assembled together. The location of the gasket ensures alignment between the brush holder assembly and the commutator, and also serves as a watertight seal at the junction between the motor housing and the gear housing. Furthermore, by retaining the gasket directly upon the brush holder assembly, it is possible to preassemble combined brush holder-gasket assemblies, eliminating a rate limiting step from the production line while providing visual quality control assurance that the gasket has been incorporated into the motor assembly during production.